This paper establishes a link between closed-loop controls for heterogeneous systems and sliding mode controls. We demonstrate that sliding mode analysis matches with experimental results from dielectric charge controllers. This approach provides a new way to analyze the behaviour of different heterogeneous systems.

This article introduces 3 Cat-1, the first project of the Technical University of Catalonia to build and launch a nano-satellite. Its main scope is to develop, construct, assemble, test and launch into a low Earth orbit a CubeSat with seven different payloads (mono-atomic oxygen detector, graphene field-effect transistor, self-powered beacon, Geiger radiation counter, wireless power transfer (WPT), new topology solar cells and WPT experiment), all fitted in a single-unit CubeSat. On one hand, this is mainly an educational project in which the development of some of the subsystems is carried out by undergraduate and postgraduate students. The satellite demonstrates its capabilities as a cost-effective platform to perform small scientific experiments and to demonstrate some of the new technologies that it incorporates.

This paper presents an active control of C-V characteristic for MOS capacitors based on Sliding Mode control and sigma-delta-modulation. The capacitance of the device at a certain voltage is measured periodically and adequate voltage excitations are generated by a feedback loop to place the C-V curve at the desired target position. Experimental results are presented for a n-type c-Si MOS capacitor made with silicon dioxide. It is shown that with this approach it is possible to shift horizontally the C-V curve to the desired operation point. A physical analysis is also presented to explain how the C-V horizontal displacements can be linked to charge trapping in the bulk of the oxide and/or in the silicon-oxide interface. Finally, design criteria are provided for tuning the main parameters of the sliding mode controller.

The objective of this chapter is to introduce the technology of Microelectromechanical Systems, MEMS, and their application to emerging energy harvesting devices. The chapter begins with a general introduction to the most common MEMS fabrication processes. This is followed with a survey of design mechanisms implemented in MEMS energy harvesters to provide nonlinear mechanical actuations. Mechanisms to produce bistable potential will be studied, such as introducing fixed magnets, buckling of beams or using slightly slanted clamped-clamped beams. Other nonlinear mechanisms are studied such as impact energy transfer, or the design of nonlinear springs. Finally, due to their importance in the field of MEMS and their application to energy harvesters, an introduction to actuation using piezoelectric materials is given. Examples of energy harvesters found in the literature using this actuation principle are also presented.

This paper introduces Diffusive Representation as a novel approach to characterize the dynamics of charge trapped in dielectric layers of microelectromechanical systems (MEMS) through a fitting process. Diffusive Representation provides a computationally efficient method to achieve an arbitrary order state-space model of the charging dynamics. This approach is particularly well
suited to analyze the dynamics of the dielectric charge under non trivial controls, as in the case of sliding mode controllers. The diffusive symbol of the experimental structure has been obtained from open-loop measurements, in which Pseudo Random Binary Sequences (PRBS) are applied to the device. The obtained model exhibits good agreement with experimental data and also allows to model the behaviour of the charge dynamics under excitation with arbitrary binary signals.

This paper reports and discusses the design and ground tests of a CubeSat payload which allows to measure, in-situ and in real time, the degradation of a polymer of electronic interest due to atomic oxygen etching in LEO. It provides real-time information on how the degradation occurs, eliminating the need to work with samples recovered once the mission has finished. The polymer, TIPS-Pentacene, is deposited on the surface of a microelectromechanical (MEMS) cantilever, which works as a resonator embedded in a Pulsed Digital Oscillator circuit. The mass losses in the polymer due to atomic oxygen corrosion produce variations in the resonant frequency of the MEMS, which is continuously sensed by the circuit and transmitted to the ground. This way, polymer mass losses around 10-12 kg can be detected during the mission. The payload is a part of the 3Cat-1 mission, a nano-satellite aimed at carrying out several scientific experiments.

Modern CMOS integrated technologies integrate a variety of complex multi-physics components which
contribute a growing number of challenges in the circuit design. This paper is focused on the description of the
requirements and technical aspects which should be considered for successful circuit design involving capacitive
MEMS. To illustrate the process, the design of an input stage for a MEMS dielectric charge bipolar control method is
presented.

Electrical models for MEMS varactors including the effect of dielectric charging dynamics are not available in commercial circuit simulators. In this paper a circuit model using lumped ideal elements available in the Cadence libraries and a basic Verilog-A model, has been implemented. The model has been used to simulate the dielectric charging in function of time and its effects over the MEMS capacitance value.

This work investigates, analytically and experimentally, the effects induced by the use of a first-order sigma-delta (S¿) feedback loop as a control method of dielectric charging for capacitive microelectromechanical systems (MEMS). This technique allows setting of a desired level of net charge in the dielectric of a MEMS device by continuously alternating the polarity of the actuation voltage. This control system displays a number of interesting effects, inherited from S¿ modulation and not usually found in conventional MEMS applications, with the charge-locking phenomenon being the most relevant. The convergence time and the effectiveness of the control method are also investigated and discussed.

The purpose of this paper is to show that sigma-delta controllers of dielectric charge can be analyzed using the tools of sliding-mode controllers, in the infinite sampling frequency approximation. This allows to study the dynamics of the hidden state variables related to the charge in the dielectric, as well as the reachability and stability of the control method. Furthermore, it is also possible to explain the response of the control bitstream as a function of the dynamical model of the system. This approach not only provides insight into the dynamics of the charge controllers, understood as hybrid systems, it also simplifies the modeling and simulations of the system.

This letter presents a double closed loop for simultaneously controlling the net dielectric charge and the device capacitance in contactless electrostatic MEMS devices. The first loop controls the net charge trapped in the dielectric layer by continuously monitoring the horizontal displacement of the C–V characteristic and applying bipolar actuation voltages to keep such net charge at the target value. The second loop adapts the actuation voltages so that the measured capacitance matches a desired value while maintaining the primary control of charge

The purpose of this paper is to show that the charge induced by radiation in a dielectric on which a sigma–delta control of dielectric charge is implemented, can be seen as a disturbance in a sliding mode controller. Preliminary experimental results are presented in which a MEMS device is irradiated with X-rays, while the dielectric charge control is continuously being monitored. The charge induced by radiation generates a change in the control bitstream, which is associated with the presence of an external disturbance on the governing control equations.

This letter investigates the capability of dielectric charge control loops to cope with charge induced by ionizing radiation. To this effect, an microelectromechanical systems (MEMS) variable capacitor has been irradiated with X-rays and gamma-radiation in three scenarios: 1) without polarization; 2) using an open-loop dielectric charge mitigation strategy; and 3) using a closed-loop control method. The results show that the charge effects induced by radiation can be partially compensated using dielectric charge control.

The aim of this paper is to formalise the term “complexity” in the context of modern microelectronics, propose the definitions of key terms and discuss a case study. Our aim is to show that the term “complex system” is implicitly related to the design of electronic systems.

This letter introduces a new second-order delta-sigma method for controlling the dielectric charge in contactless capacitive microelectromechanical systems. This method improves the one previously proposed by the authors, providing second-order quantization noise shaping and avoiding the plateaus typical of first-order strategies. The feasibility and the features of the new method are demonstrated both experimentally and through simulations.

This paper presents a new method to characterize the dynamics of the charge trapped in the dielectric layer of contactless microelectromechanical systems. For sampled-time systems, this allows knowing the state of the net charge at each sampling time without distorting the measurement. This approach allows one to model the expected behaviour of dielectric charging as a response to a sigma-delta control of charge. The goodness of the proposed approach is obtained by matching the experimentally obtained closed loop response with the one predicted using the proposed characterization method. The characterization method also provides a criterion to avoid nonlinear effects, such as fractal-like behaviour, in charge control.

In this paper, we present a new closed-loop control method of dielectric charge for contactless capacitive microelectromechanical systems. The method uses a feedback loop to maintain the net charge in the dielectric layer at the desired level. We show that, under particular conditions, the control loop is similar to a thermal sigma-delta modulator as used in thermal sensors. In this way, the control actuation will inject an average charge into the dielectric to keep it at a desired level while applying an actuation bit stream to compensate the charge being continuously leaked out of the dielectric. The validation of the method is carried out employing numerical simulation and experimental measurements of Poly-MUMPS devices. [2013-0217]

This paper presents the first results obtained with devices fabricated on the inaugural run of the new Piezo-MUMPS process. The main objective was the design of resonators for energy harvesting and chemical sensing applications

Dielectric charging of insulating films in microelectromechanical
systems (MEMS) has a crucial effect on the
operation of those devices. A new method has been presented
for the purpose of characterizing the dynamics of the charge
trapped in the dielectric layer of MEMS devices. This allows
knowing the state of the charge at each sampling time without
distorting the measurement.

Charging of dielectric materials in microelectromechanical
systems (MEMS) actuated electrostatically is a major
reliability issue. In our previous work we proposed a feedback
loop control method that is implemented as a circuit and that
allows smart actuation for switches and varactors. In this paper
we discuss system-level modeling of MEMS devices including
all aspects of the system: proposed control method, charging
dynamics and realistic models of the mechanical components of
MEMS.

A new dynamical closed-loop method is proposed to control dielectric charging in capacitive microelectromechanical systems (MEMS) positioners/varactors for enhanced reliability and robustness. Instead of adjusting the magnitude of the control voltage to compensate the drift caused by the dielectric charge, the method uses a feedback loop to maintain it at a desired level: the device capacitance is periodically sampled, and bipolar pulses of constant magnitude are applied. Specific models describing the dynamics of charge and a control map are introduced. Validation of the proposed method is accomplished both through discrete-time simulations and with experiments using MEMS devices that suffer from dielectric charging.

This paper introduces a new actuation scheme for implementing Pulsed Digital Oscillators (PDOs) for electrostatic MEMS resonators. In this scheme, the capacitance of the device is
biased with a voltage and it is periodically sampled. Short pulses of zero voltage are applied depending on the decisions taken by the oscillator loop. The paper discusses in detail the implementation of such electrostatic PDO (e-PDO) through a prototype and links the e-PDO to the conventional PDO theory. As an example, it is shown that with this actuation scheme it is possible to excite different resonances of the mechanical structure simply by changing the parameters of the feedback filter of the oscillator.

This paper extends our previous work on the selective
excitation of mechanical vibration modes in MEMS devices using
pulsed digital oscillators (PDOs). It begins by presenting extensive
simulation results using the set of iterative maps that model the
system and showing that it is possible to activate two or three spatial
modes (resonances) of the mechanical structure with a PDO.
The second part of this paper presents experimental results corroborating
the theory and simulation results. It is shown that it is
possible to separately excite vibration modes of the device by setting
a few parameters of the PDO structure such as the sampling
frequency and the sign of the feedback loop.

The aim of this paper is to show that it is possible
to excite selectively different mechanical resonant modes of a
MEMS structure using pulsed digital oscillators (PDOs). This
can be done by simply changing the working parameters of the
oscillator, namely its sampling frequency or its feedback filter. A
set of iterative maps is formulated to describe the evolution of the
spatial modes between two sampling events in PDOs. With this
lumped model, it is established that under some circumstances
PDO bitstreams related to only one of the resonances can be
obtained, and that in the anti-oscillation regions of the PDO
the mechanical energy is absorbed into the electrical domain on
average. The possibility of selecting for a given resonant frequency
the oscillation and anti-oscillation behavior allows one to obtain
oscillations at any given resonant mode of the MEMS structure.

The objective of this work is to show that is possible to excite different vibration modes of MEMS resonators using Pulsed Digital Oscillators. This class of circuits exhibit two different behaviours: the oscillation and the anti-oscillation mode. In the oscillation mode, th eoscillator in average provides energy to the resonator, whereas in the anti-oscillation mode, it extracts energy of the resonator until a limit cyucle is reached near the origin. It will be shown that by preparing suitable PDO configurations it is possible to selectively excite different resonant modes of MEMS resonator. The exprimental corroboration has been obtained with a scanning Doopler vibrometer.

This work shows the application of Pulsed Digital Oscillators to the detection of physical changes in MEMS devices that cause small shifts in their resonance frequencies. Such devices can be used as resonators in several sensor applications. According to this, a case study using a PDO structure to measure small concentrations of volatile organic gas compounds (VOC’s) introduced here. The MEMS devices used are cantilevers with a
thin layer of polymer sensitive to the VOC concentration.
Such devices have been simulated with the Coventor software to see the influence of the polymer layers on their mechanical responses.
Finally, experimental measurements with various VOCs have
been done, and results extracted from two PDO system sources,
digital and analog, have been analyzed and compared.

In this paper we present an electronic circuit for position or capacitance estimation of MEMS electrostatic actuators based on a switched capacitor technique. The circuit uses a capacitive divider configuration composed by a fixed capacitor and the variable capacitance of the electrostatic actuator for generating an output signal that is a function of the input voltage and capacitive ratio. The proposed circuit can be used to simultaneously actuate and sense position of an electrostatic MEMS actuator without extra sensing elements. This approach is compatible with the requirements of most analog feedback systems and the circuit topology of pulsed digital oscillators.

Pulsed digital oscillators (PDO) are sampled nonlinear structures that include a resonator device, a one-bit quantifier and a feedback loop with n-delays. PDOs can be used in a wide range of frequency-based sensing applications. This paper describes for the first time the application of PDOs as self-sustained oscillators in gravimetric sensors for volatile organic compounds (VOC) detection and measurement. For this application, the device is a MEMS cantilever with a polymer layer deposited on top of it. The deposited layer is mass-sensitive to the concentration of VOC, so that the concentration of VOC changes the oscillation frequency of the PDO. Two different polymeric materials have been tested: poly-epichlorohydrin (PECH) and poly-dimethylsiloxane (PDMS). Our results show that low concentrations of toluene and octane can be detected successfully. The practical influence of parameters, such as the MEMS damping losses on the sensor performance are also analyzed and experimentally tested. These are the first experimental results showing how PDOs can successfully track changes in the resonant frequency of MEMS resonators. (C) 2008 Elsevier B.V. All rights reserved.

The objective of this work is to analyze pulsed digital oscillators (PDOs), as dynamical systems. It is proved that under some conditions, the bitstream at the output of the oscillator is that of the sign of a sampled sinusoid at the resonant frequency of the resonator, and that a bijection exists between these sequences (without distinguishing between a sequence and its negated version) and those of first-order sigma-delta modulators. This provides a new and simple method of obtaining the oscillation frequency of PDOs just from their bitstream.

The objective of this work is to extend the linear analysis of Pulsed Digital Oscillators to those topologies having a Finite Impulse Response (FIR) in the feedback loop of the circuit. It will be shown with two specific examples how the overall response of the oscillator can be adjusted to some point by changing the feedback filter, when the resonator presents heavy damping losses. Extensive discrete-time simulations and experimental results obtained with a MEMS cantilever with thermoelectric actuation and piezoresistive position sensing are presented. It will be experimentally shown that the performance of the oscillator is good even below the Nyquist limit.

This paper describes new theoretical and experimental results showing that the pulsed digital oscillator, a set of sigma–delta-based oscillator structures for MEMS recently introduced by the authors, can maintain a good oscillation behaviour even for sampling frequencies below the Nyquist limit. Specifically, the theory is extended to the undersampling region and the complete set of ‘perfect’ frequencies (sampling frequencies at which the oscillation frequency is the natural frequency of the resonator) is analyzed. Therefore, an extension of the use of this kind of oscillators to high frequency applications becomes straightforward.